Apparatus for toning tacky surfaces

ABSTRACT

A toner applicator comprising a housing for containment of toner, at least one free-moving weight within said housing for breaking up toner aggregates and agitating the toner, separable pad members forming a bottom wall of the housing and releasing said toner upon separation thereof, and said members being hingedly mounted whereby to adapt to distributing a mound of said released toner across an image area to be developed of a surface having imagewise tacky and nontacky areas.

This is a division of application Ser. No. 605,541, filed Aug. 18, 1975.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention relates to image reproduction systems and moreparticularly to image reproduction systems involving the application oftoner particles over a tacky surface to develop a latent image.

2. Description of the Prior Art

The advent of electrophotography and wide acceptance of theelectrostatic reproduction method have resulted in a large number ofprocesses and devices useful in the application of toner particles on anelectrically charged surface. Mechanisms and associated methods such ascloud chambers, cascade developers, transfer brushes, and rollers arewell known. In general, some means are usually provided to meter theamount and/or rate of toner application.

In the graphic arts area, a system of image reproduction has beenemployed, whereby a photosensitive element is first exposed to actinicradiation in an imagewise exposure. The element exhibits a differentdegree of tackiness as a result of this exposure. The latent image canbe developed through a process called toning, whereby toner particlesare distributed over the surface of the element and adhered to the tackyareas. A typical such element and associated process, capable ofproducing multi-colored images is described in V. F. H. Chu et al, U.S.Pat. No. 3,649,268 and the patents referred to therein, while adescription of a typical toning method is found in M. Burg et al, U.S.Pat. No. 3,060,024.

It has also been known in the art to use a small pad having a handle onone side and a thick pile, such as lambswool, on the other, to apply anddistribute the toner over the latent image-bearing surface. The pad isdipped in a dish containing a supply of toner; it is then rubbed lightlyand repeatedly in an S-type path over the latent image-bearing surface.Toner particles adhere to the tacky areas and the image is thusdeveloped.

Another practice has been to first apply the toner by patting a paddipped in toner all over the surface and then using it to rub thesurface with an S-type motion as before. This practice is slow, untidy,and generates an objectionable dust cloud during the patting operation.Results generally lack reproducibility.

Rotating, or combinations of rotating and oscillating cylindricalbrushes used to embed a toner in the soft areas of an imagewise exposedsurface have also been tried in the prior art, and a good summary of thevarious alternatives will be found in R. W. Jones et al, U.S. Pat. No.3,723,123.

Both electrostatic and tacky surface image development involve theapplication of toner particles over a latent image-bearing surface. Inthat respect there is a similarity in the problems encountered,especially the problems relating to the dispensing of toner particles.However, systems using the tacky surface principle, be it a situationwhere the toner particles simply adhere to the surface or are embeddedtherein, present an additional problem. The amount of toner adhered tothe tacky surface tends to vary, depending on the delivery rate andmethod or distribution over the surface. This is particularly noticeablewhere the toning step is done manually, resulting in nonreproducibledevelopment. Additionally, the softer, tacky surface is vulnerable toscratching.

In an effort to eliminate these problems, the patting method and rollerapplicators have been introduced, but with questionable results.Problems still unsolved are uniformity of density over large, said colorareas, dust clouds, reproducibility and ease of handling.

A need for a simple and reliable method to reproducibly distribute tonerover a tacky surface still persists.

SUMMARY OF THE INVENTION

According to the invention there is provided an apparatus for thedevelopment of a surface, at least portions of which are tacky,comprising arranging toner particles in the form of an elongated moundon a section of said surface and then distributing said toner particlesover said surface by pushing the elongated mound of toner particlesacross said surface with at least one pad with at least a portion of themound beneath the pad (esp., the leading edge thereof), whereby thedistributed toner particles become adhered to the tacky portions of saidsurface. The development is completed by wiping off excess toner fromthe surface. The surface is preferably an imagewise exposedphotohardenable layer. In this case the toner becomes imagewise adheredto the surface.

In a preferred process, the pad is moved across the surface in acurvilinear path pushing the elongated mound of toner particles in frontof it. The curvilinear path may be sinusoidal, serpentine, spiral,elliptical, figure eight, S, or other patterns.

There is further provided according to this invention an applicatorapparatus for the development of an imagewise exposed element with asurface having imagewise tacky and nontacky areas comprising a housingfor containment of toner, at least one free-moving weight within saidhousing for breaking up toner aggregates and agitating the toner, meansto release toner from the housing, and at least two hinged pads mountedon the housing.

The apparatus may further comprise an additional cleaning pad,detachably mounted over the applicator pads to remove excess toner fromthe surface of the exposed element.

The described apparatus overcomes the problems of the prior art in asimple manner. By confining the deposition of the toner to a relativelysmall area of the total surface, the dust problem can be effectivelycontrolled. What is more surprising is that the subsequent distributionby the applicator pad over the remaining surface results in areproducible, generally streak-free, and uniform density image.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic of a pad and toner particles as the pad ismoved over the imagewise exposed surface.

FIG. 2 shows a schematic of the typical prior art method of applyingtoner through a pad over an imagewise exposed surface.

FIG. 3 is a schematic representation of a typical arrangement for theprocessing of an imagewise exposed element in accordance with thisinvention.

FIG. 4 shows an applicator device particularly well adapted for themanual performance of this process.

FIG. 5 is a schematic representation of the applicator device shown inFIG. 4 in operation.

FIG. 6 is a schematic representation of the combined demountablecleaning pad and applicator device of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In practicing the invention, a photohardenable element useful in animage reproduction process of the type disclosed in Chu et al, U.S. Pat.No. 3,649,268, may be selected. Such an element, which preferablycomprises a photopolymerizable layer on a sheet support, following animagewise exposure, will bear on its surface a latent image comprised ofimagewise tacky and nontacky areas. Development of the image is obtainedby distributing toner particles over the latent image-bearing surface.The toner particles tend to adhere on the tacky sections to render thelatent image visible. The toner is comprised of particles, especiallypigment particles, which may be colored to produce a color image. Auniformly tacky surface such as an unexposed photohardenable element ora board coated with partially dried shellac may also be toned accordingto the invention.

In the preferred embodiment of this invention, the photosensitiveelement is imagewise exposed to produce a latent image of tacky andnontacky areas on the surface of the element. It is then placed in aprocessing tray or simply a flat table top.

A quantity of toner particles in excess of that required to develop theimage on the surface, or section thereof to be toned, is first depositedon the surface, preferably onto a conveniently located small area of thesurface of the element being processed. By mode of depositing or pushingwith a pad, the toner particles can be arranged in the form of a narrow,elongated mound. Such an area may be in the upper right hand corner, butof course any location on the surface or even outside the surface of theelement is satisfactory, the choice being a matter of personalpreference of the individual operator.

A detailed description of an apparatus particularly well adapted to thedispensing of toner particles is given later in this description.However, any hopper capable of delivering a quantity of toner particlesto the form of an elongated, narrow mound within a relatively confinedarea, and without the release of significant dust in the environment isacceptable.

In the preferred apparatus, the toner is contained in a housing withmovable pads on one side and containing a free-moving weight. To depositthe toner, the housing while lying on the proof is rapidly oscillatedwhile holding the movable pads apart.

Once the toner has been deposited and arranged in the form of anelongated mound, it is distributed over the surface by pushing the moundalong with a pad. A pad 10 may be used as shown in FIG. 1. The pad whichpreferably includes a handle 11 and a resilient underlayer 12 such aselectrostatically flocked foam rubber, may be guided in a curvilinearpath (especially, an S-type path) with a rocking motion over the exposedsurface tracing a path which covers all of the surface. One completecoverage constitutes a cycle and more cycles than one may be used toobtain the desired color density and uniformity in the developed image.As described hereinafter, a pair of parallel pads is preferred.

For purposes of this invention, the rocking motion is defined as thelifting of one edge of the pad during the distribution of the tonerwhile the pad is moved over the surface in one direction, and then thelowering of that edge and lifting of the other as the pad movementdirection is reversed during the tracing of the S-type path over theexposed surface as shown in FIG. 1. This rocking motion results inmaintaining the toner particles in a narrow mound 13 that extends allalong the line of contact of the leading edge of the pad and the exposedsurface of the processed element regardless of the relative direction ofthe pad over the surface. At least a portion of the mound is thereforebeneath the part of the pad which is above and forward of the line ofcontact of the pad with the surface. As a consequence, the pad glidesover a freshly adhered layer of toner 14, which has been withheld by thetacky areas from the mound of toner as it was pushed over the surface.This freshly adhered toner layer acts as a protective barrier betweenthe pad surface and the sensitive tacky areas to prevent scratching ofthe tacky surface. In addition, since there is always an excess amountof toner in the moving mound, the tacky areas will constantly withholdthe precise amount of toner needed to render them nontacky bysaturation. Final density, therefore, tends to be reproducibly moreuniform all across the toned areas.

The final step involves simply wiping off any excess toner lingeringover exposed and unexposed areas of the surface of the element. A brush,lamb's wool pad, acrylic, deep pile fabric pad, cloth or even vacuum maybe used to remove this nonadhered toner. The material selected willdepend on matching the triboelectric properties of the pad, toner, andsurface of the toned element. An acrylic pad is preferred, which iswiped over the surface in a series of long, uniform and continuouswiping moves from one end of the element to the other; the pad may becleaned by passing it over a vacuum cleaner between wiping cycles.

FIG. 2 shows for comparative reasons the standard method of using a padto distribute toner over the tacky surface. Toner particles are eithersprinkled over the imagewise exposed surface or the pad itself may befirst dipped into a container with toner; in either case during thedistribution step of the development toner particles are randomly spreadunder the pad 15 which pushes the toner particles hard into and over thesensitive areas 16, of the tacky surface 17, resulting innonreproducible development.

An applicator device adapted to practice this invention, comprising ahousing for containment of toner particles, a free-moving roller withinsaid housing for breaking up toner aggregates and agitating the toner(whereby it is positively dispensed), means to release toner from thehousing, and at least two hinged pads mounted on the housing is shown inFIG. 4.

The device includes a housing 18, which is shaped somewhat like aninverted U-shaped trough, to provide an easy hand hold for the operator.The upper section of housing 18 is a removable cover 19 which isremovably secured by a spring clip 20. On the lower end of the housingthere is affixed a skirt 21 which tends to prevent the operator'sfingers from inadvertently interfering with the operation of theapplicator mechanism located below the skirt. In addition, this skirttends to somewhat prevent loose flying toner particles from beingreleased to the environment.

The lower part of the housing is open. The opening is, however, blockedby two applicator pads which in their normal position completely closethe bottom of the housing and prevent any toner particles from escaping.

In the following description only one side of the applicator is shown.Identical complementary parts are also located on the opposite side andcomplete the mechanism.

The applicator pads 22 and 23 have an inner, rigid flat core 24 having agenerally rectangular cross section, are covered on the outside with aresilient material and have a soft fabric or pile surface. Two tangs 25and 26 are mounted perpendicular to the rigid core 24 and serve torotatably attach pads 22 and 23 to the lower end of the housing. Theattachment is accomplished through pins 27 and 28 respectively. Pins 27and 28 extend beyond the full length of the pad and protrude outside thehousing through openings in its sidewall 29. Pin 27 extends outside thehopper sidewall through slot 30 while pin 28 extends through the samewall 29 through a circular close fitting hole. This arrangement allowspad 22 to move laterally in addition to the rotary motion possible ofboth pads 22 and 23.

On the outside of side wall 29 of the housing there is mounted a bracket31 shaped somewhat like an inverted T. The horizontal section 32 ofbracket 31 bears a hole, and a slot shown by numeral 33 in FIG. 4. Pin27 is inserted through the hole while pin 28 fits through slot 33. Ahelical tension spring 34 is strung between pins 27 and 28, on theoutside of horizontal section 32 of bracket 31, pressing the pinsagainst the inner side of the bracket holes, set at such a distance asto maintain the two pads 22 and 23 in contact with each other.

A manually depressible handle bar 35 on the side of the housing isattached to bracket 31 by an arm 36. Bracket 31 is brought above theskirt 21 through a slot 37 in that skirt on the side adjacent side wall29. This arrangement permits the lateral motion of bracket 31 whenhandle bar 35 is pushed in the direction of the hopper. Since pad 22 isattached to bracket 31 through pin 27, it follows the movement of thehandle bar. Spring 34 tends to restore pad 22 to its original positionwhen handle bar 35 is released. This arrangement provides means forreleasing toner from the housing.

Inside the housing and resting on pads 22 and 23 is a heavy roller 38which extends almost the full length of the housing. As the pad is movedlaterally, first in one direction then in the other, inertia tends tomove roller 38 in a path limited by pins 27 and 28. Such path brings theroller successively over pad 22 and 23 passing over the point of contactbetween them. When handle bar 35 is pushed toward the housing, pad 22has been moved laterally away from pad 23 creating an opening in theform of a slot extending the full length of the housing. The passage ofroller 38 over this slot forces toner particles through the slot ontothe surface below.

Two wire restrainers 39 are strung across the width of the housing toprevent the roller 38 from falling back and possibly forcing the housingcover 19 open, when the applicator pad is turned upside down or laid onits side.

In the preferred embodiment, a transparent, plastic material is used forthe housing, and cover 19 of the applicator device. Stainless steel isused for bracket 31, handle bar 35, roller 38 and other metal parts ofthe device. An electrostatically flocked foam rubber was chosen as thecovering of pads 22 and 23. The materials described are exemplary onlyand individual items may be replaced by others having more desirablecharacteristics from the engineering or economic point of view.

The device described above may further include a provision fordetachably mounting thereon an additional pad 41 with upper recess asshown in FIG. 6 which encloses the lower portion of the device on allfour sides. Such pad may simply comprise a rectangular rigid block whichbears on its lower surface 42 an acrylic pile 43. On the opposite sidethere may be provided a cavity 44 of sufficient size to contain thelower part, including skirt 21 of the toner applicator shown in FIG. 4.In this case a mating means must be provided both on pad 41 and thetoner applicator. Such means may comprise two small metallic tabs 45 and45' affixed on the sidewalls of the toner applicator 46. Two smallmagnets 47 and 47' embedded in the body of pad 41, adjacent surface 48provide sufficient holding power when the metal tabs 45 and 45' arebrought in close proximity to demountably attach pad 41 to applicator46. This arrangement has the advantage of providing a clean andprotected storage facility for the applicator pads 22 and 23 of thedevice, which are normally saturated with toner and present a staininghazard if left unprotected.

Pad 41 is used for the cleaning cycle which completes the processing ofthe imagewise exposed element.

In operation, following exposure to actinic radiation, the element isplaced on a flat surface for processing. A typical processing area isshown in FIG. 3 and may comprise a flat tray 49 on which is mounted theexposed element 50. The tray may provide a number of storage bins 51 onone side where toner applicator devices containing toners of variouscolors may be stored. As shown in FIG. 3, once the toner applicator 46is removed from the cleaning pad 41, the pad 41 may be left in thestorage bin. A complete assembly of applicator and cleaning pad is shownby numeral 52. Near the exit of each bin, there may be located a slot 54which is connected to a vacuum cleaning system 53. Thus the lower partof the cleaning pad may be drawn over the slot both when inserted andremoved from the storage bin as well as between cleaning strokes toremove any adhering toner particles.

Toner applicator 46 is preferably placed on the upper right hand cornerof the exposed element 50 and in contact with the surface. It is thenshaken vigorously back and forth while the operator depresses handle bar35. This action both opens a slot at the bottom of the housing andforces roller 38 to move back and forth within the housing, breaking uptoner caking and pushing toner particles onto the surface below. Becauseof the two pads present, the amount of toner released is limited to thevolume defined by the two pads, the housing, and the surface of theelement, and tends to be confined into an elongated mound under theslot. Once an excess amount of toner has been released, determinedprimarily by the number of back and forth vibrations imparted to theapplicator, handle bar 35 is released and the actual processing of theelement begins. The rocking motion of the pads maintains the mound oftoner in a slightly compact condition.

The two pads, 22 and 23, below the housing are hinged on pins 27 and 28and thus tend to swing around the axis of pin 27 and pin 28 as theapplicator is moved over the surface of the exposed element. The extentof the swing is limited by the lower end of the housing as shown in FIG.5. When the applicator is moved in the direction of the arrow in FIG. 5,leading edge 56 of pad 23 pushes the toner mound 57 over the exposedsurface, while leading edge 58 of pad 22 forms and pushes a secondsmaller mound of toner 59. Due to the curvature of the pads, an acuteangle (e.g., 3°-45°) is formed between the leading edges of the pads andthe surface wherein at least a portion of the mounts 57 and 59 iscontained in a slightly compact condition in front of the line ofpad-to-surface contact and beneath the leading edge of each pad. Themound of toner 59 is created by toner particles carried by the pads andtoner which escaped in the vicinity of the applicator during the tonerreleasing operation. It should also be noted that both pads have theirlower surface completely covered with toner, as a consequence of thetoner releasing operation, thus serving as a source of material for thecreation of the smaller mound ahead of the leading pad.

As the applicator is guided laterally over the processed surface, itpushes a long narrow mound of toner just ahead of the point of contactbetween the pad and the sensitive surface. Since no pressure is appliedover toner mounds 57 and 59, the tacky surface underneath will withholdalways the same amount of toner as the mound moves over it. This amountwill be precisely what is needed to render it nontacky, thus resultingin toner conservation through minimized waste.

When the applicator reaches point 55 in FIG. 3, the device is slideablymoved in the direction of the arrow along the dotted path and theprocess is reversed. Since the pads 22 and 23 are symmetrical,previously lagging edge 60 becomes the new leading edge, pushing thesmaller mound of toner while the now leading edge 61 pushes the largermound. Thus, as the pad describes an S-type path over the exposedelement, there is always a mound of toner preceding the point of contactbetween the pads and the sensitive surface.

As shown by the dotted line in FIG. 3, more than one complete cycle maybe required to obtain the final degree of density uniformity desired. Inaddition, there may be need to release more toner, if the originalquantity proves low. However, this is not critical and may be performedany number of times without adverse effect.

Once the desired degree of uniformity and density has been obtained,applicator 46 is attached to cleaning pad 41 which is preferably drawnover the vacuum slot 54 to remove any lingering dirt or toner. Then thepad is used to wipe off excess toner from the surface of element 50. Inorder to avoid staining the reverse side of element 50 it is preferredthat excess toner be first removed from around the edges of thiselement, the center being left to the end. Experience has shown thateven though an excess amount of toner is initially dispensed, totaltoner consumption is less than what is used when the sprinkling orpatting methods are used, because the toner is adhered only to the tackysurfaces and almost none wasted over the nontacky areas.

The method of this invention is not limited by the embodiments describedabove. In an alternate approach a V-shaped resilient applicator may beemployed, having an integral or even separate toner releasing mechanismand riding over guides attached to the processing area. Such applicatorand guide combination could be used to push the toner across thesensitive surface of an exposed element and then lift the pad at the endof the travel and lower it behind the toner mound; so that, uponreversing the direction in which the pad travels, the toner mound willagain be ahead of the point of contact between the sensitive surface andthe applicator.

The element described in Chu et al, U.S. Pat. No. 3,649,268 is animaging element known as positive working. What is meant by this term isthat upon exposure, the areas that do not receive any actinic radiationbecome tacky, so that toner adheres to the nonexposed areas. However,this toner application method and associated equipment is equally usefulfor the development of negative working systems, i.e., systems in whichthe toner receptive areas are those which have been subjected to actinicradiation, such as described in pending application No. 583,456, byCohen et al.

Control Test

A photopolymerizable element similar to that of Example I, U.S. Pat. No.3,649,268 was prepared having 0.0003 inch (˜0.0076 cm.) photopolymerlayer coated on 0.005 inch (˜0.0013 cm.) polyethylene terephthalatesupport, with the other side of the photopolymer layer covered with a0.00075 inch (˜0.0019 cm.) polypropylene film as a cover sheet. As inExample I, U.S. Pat. No. 3,649,268, the cover sheet was removed, thephotopolymer layer laminated to Kromekote, (cast coated on side) coverpaper, and exposed to actinic radiation.

A pattern comprising among other images, fourteen solid square testareas, about two by two inches (˜5 × 5 cm.) evenly dispersed over a 17by 24 inch (43.2 × 61 cm.) test sample was used to compare thereproducibility and uniformity resulting through the use of the methodand apparatus of this invention against that of the prior art.

Twelve samples were prepared using the above target. Each sample wasgiven the same exposure. Various operators were used in processing sixof the samples, using the technique common in the prior art. Thisinvolves first placing the exposed element on a flat surface, preferablya processing tray, and using a pad with an acrylic pile of the typeshown in FIG. 2. The pad was dipped in a tray containing a powdered cyantoner. It was then placed over the surface of the exposed element, andstarting from the top right hand corner, guided over the surface of theelement in an S-type path. This path constituted one full cycle.Starting from the end point of the first cycle, a second cycle wascompleted in a path at right angle to the first. The process continueduntil 20 cycles were performed. Following this, the surface of theelement was cleaned using a piece of antistatic treated flannel cloth.

A conventional reflection densitometer was used to measure the resultingdensities in each of the fourteen squares, and the average and meandeviation was computed for each sample. The following Table I summarizesthe results.

                  Table I                                                         ______________________________________                                        Operator Average Density  Mean Deviation                                      ______________________________________                                        A        1.55             0.02                                                A        1.61             0.04                                                B        1.74             0.02                                                B        1.71             0.03                                                C        1.68             0.03                                                C        1.66             0.02                                                ______________________________________                                    

If one takes the average of the mean deviation of the density to be ameasure of the uniformity obtained by an operator in an averageprocessing, one gets a quantitative figure for comparison. Here thismeasure equals 0.027 density units. Also, a measure of reproducibilityof this uniformity as operators and samples vary can be computed bytaking the average of the average density of each sample and computingthe mean deviation, which in this case results in 0.053 units.

EXAMPLE I

The same material, test target and measurements were repeated as forcontrol test I above. Processing was done using a device substantiallysimilar to the device shown in FIGS. 4, 5 and 6. It was found that 8cycles rather than 20 were required to obtain the desired density.Results are summarized in Table II.

                  Table II                                                        ______________________________________                                                 Average Density Mean Deviation                                       Operator (Density Units) (Density Units)                                      ______________________________________                                        A        1.51            0.02                                                 A        1.52            0.04                                                 B        1.53            0.03                                                 C        1.51            0.02                                                 C        1.53            0.02                                                 C        1.52            0.02                                                 ______________________________________                                    

Similarly, taking the average of the mean deviation as a measure ofuniformity of density regardless of operator, we find that the measurefor uniformity equals 0.025 density units while a computation of themean deviation of the average density from operator to operator which isa measure of the reproducibility of the processing, equals 0.007 densityunits.

What is claimed is:
 1. A toner applicator apparatus comprising a housingfor containment of toner, at least one free moving weight within saidhousing for breaking up toner aggregates and agitating the toner, a pairof separable applicator pad members forming the bottom wall of saidhousing, means to imparttranslation to said members to open and closesaid housing thereby releasing said toner onto a substrate to bedeveloped, said pads being hingedly mounted to facillitate applicationof a mound of said released toner to the image areas of said substrateupon functional movement of said apparatus over said substrate, and atleast two hinged pads mounted on the housing.
 2. A toner applicatoraccording to claim 1 wherein said free moving weight is a bar or roller.3. A toner applicator according to claim 2 wherein said means for movingsaid pads apart from each other comprised a manually operable bar on theside of the housing.
 4. A toner applicator according to claim 3 whereinsaid pads have a soft fabric or pile surface.
 5. A toner applicatoraccording to claim 4 detachably mounted on top of a pad which enclosesthe lower portion of said applicator.
 6. A toner applicator according toclaim 3 wherein said pads have an electrostatically flocked foam rubbersurface.